Portugal installs solar telescope at Paranal Observatory to study exoplanets

In the Atacama Desert, in northern Chile, the altitude, low humidity and atmospheric stability make the Paranal Observatory one of the most privileged places in the world for observing the cosmos. It was there that, in early April, a telescope built in Portugal pointed at the Sun for the first time. This was no symbolic gesture: it was the culmination of years of engineering work, developed from scratch by the Institute of Astrophysics and Space Sciences (IA), which designed, built and installed the PoET (Paranal solar ESPRESSO Telescope) at one of the world’s most prestigious astronomical observatories, the European Southern Observatory (ESO) complex.

From conception to operation, the PoET is entirely the work of the IA, which developed both hardware and software in Portugal with the involvement of teams from the Faculty of Sciences of the University of Lisbon (FCUL) and the Centre for Astrophysics of the University of Porto (CAUP/FCUP). Whilst some components were manufactured in Portugal, the main telescope was produced in Italy, and the dome was built by a Chilean company; the architecture, the intelligence, and the coordination of the project are Portuguese.

The instrument has a diameter of 60 centimetres and observes specific regions of the Sun — individual sunspots, magnetic structures and zones of intense activity. Simultaneously, a second, smaller telescope captures the light of the entire solar disc. The data travel nearly 75 metres of optical fibre to reach ESPRESSO, one of the world’s most precise spectrographs, installed on the Very Large Telescope (VLT) at the ESO.

It is a chain of precision, designed to answer a fundamental question: what can the Sun teach us about other stars — and about the planets that orbit them? Most exoplanets are discovered through subtle variations in starlight. But those stars are not passive objects: they are subject to what is known as “stellar noise”, which can mimic — or conceal — planetary signals. As Nuno Cardoso Santos, Principal Investigator of the PoET, explains: “One of the greatest challenges in the search for other Earths is the astrophysical ‘noise’ generated by the host stars themselves. The PoET’s observations could be fundamental in revealing and characterising exoplanets that may currently be hidden within that noise.”

Until now, there was no effective way to separate that noise from a planet’s signal. The Sun, being the star we know best and the only one we can observe in detail, is the ideal laboratory for learning to read that noise. “We will use the Sun almost as a guinea pig to try to understand other stars,” says Alexandre Cabral, professor at FCUL and head of the IA’s Instrumentation and Systems for Astronomy team. What is learned here will be applied to the study of distant stars and, potentially, to the discovery of other planets.

The PoET now operates fully automatically and is controlled remotely from the Centre for Astrophysics of the University of Porto. The solar data collected by the PoET and analysed by ESPRESSO will be made available to the international scientific community through the ESO Science Archive, making this Portuguese instrument a tool for global use.

The project is part of an integrated strategy. The PoET was funded by the FIERCE project, supported by the European Research Council, whose central aim is precisely to resolve the problem of stellar noise that limits the detection of exoplanets. Portugal’s commitment to the ESA missions PLATO and ARIEL is also part of this broader strategy.

“The PoET is part of a long-term strategy. The scientific results of the FIERCE project will be essential for missions to which Portugal is already committed, such as PLATO and ARIEL. The IA is not building isolated instruments — it is building knowledge that will serve an entire generation of telescopes and missions,” says Ricardo Conde, President of the Portuguese Space Agency.